[DOC] flat_object filed supports wildcard query since 2.18

[kkewwei]

What do you want to do?
https://opensearch.org/docs/latest/field-types/supported-field-types/flat-object/#supported-queries

https://github.com/opensearch-project/OpenSearch/blob/2.18.0/server/src/main/java/org/opensearch/index/mapper/FlatObjectFieldMapper.java

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
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Tell us about your request. Provide a summary of the request.

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.